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Andarine S4



Ostarine MK-2866

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05 Jan 2013 Clinical Research Pharmaceuticals firm Galpagos has chosen a candidate drug to enter trials for the treatment of a weight loss disease.

Ostarine - SARMs Profile

ostarine structure

(a/k/a/ SARM-4, S-4)

Family: Selective Androgen Receptor Modulator

Half Life: About 4 hours

Formula: C19 H18 F3 N3 O6

Chemical Structure: S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide

Anabolic Rating: Similar to Testosterone Propionate 

Facts: Ostarine (*S-4) is a Selective Androgen Receptor Modulator produced by GTx Inc, which is currently in the investigational stages of development. A SARM is exactly what it sounds like: a compound (not an anabolic steroid) which has the ability to stimulate the androgen receptor (much the same way as anabolic steroids). Unfortunately, due to its status as a drug still in the developmental stage, most of the research on it has been done in rodents and trials only. 

S-4 is an orally active (and highly bioavailable) selective agonist for androgen receptors which was shown to have anabolic effects in muscle and bone tissue. It has been shown to have no measurable effect on lutenizing hormone (LH) or follicle-stimulating hormone (FSH), but it has been shown to have some effect on prostate weight, with an androgenic potency around 1/3rd of its anabolic potency (1). Still, this is a good trade-off, because it’s anabolic effect has been measured to be roughly the same as testosterone. It has also been shown to produce dose-dependent increases in bone mineral density and mechanical strength in addition to being able decrease body fat and increase lean body mass (2). 

Unfortunately, it has a short half-life in humans of only 4 hours (3), and thus far has only gone through phase II clinical testing in humans (4).  

Practical Use: This compound has potential use for all aspects of male hormone replacement therapy, and could eventually replace testosterone for this purpose. Since there is currently no accepted test for SARMs, athletes who are subject to drug testing would find it to be a suitable replacement for anabolic steroid use. Since it doesn’t effect LH or FSH, it may also be a highly useful anabolic agent to be used while attempting post-cycle therapy. 

Side Effects: Prostate enlargement (1/3rd of what is seen with testosterone) and potential acne are potential side effects, although most users don’t report either of them; much more common are vision problems (floaters, yellow-tinged vision). Water retention, gynecomastia, and most other steroid-related side effects are probably not possible. In addition, inhibition of natural hormone levels is probably minimal or nonexistent at worst.

Used By: I’ve successfully used S-4 and can attest to its potency and lack of side effects – but since it has only recently appeared on the black market (in very limited quantities), very few people have gotten the opportunity to try it. I suspect that some high-level athletes have gotten their hands on it, as have a small handful of bodybuilders. In the coming years we can expect it to become an accepted part of the underground pharmacopeia. 

Typical Dose: I’ve tried several different dosing protocols with this drug, ranging from only pre-workout, to only post-workout, to every day and every other day. For me, 100 milligrams prior to workouts and 100 milligrams in the morning (on non-workout days) appears to work best.

Stacks Well With: S-4 can be used in place of testosterone in virtually any cycle. In a very practical sense, because it causes no water retention, I suspect that it will be used very successfully in the final stages of pre-contest cycles for bodybuilders (or as a very potent stand-alone for athletes under doping controls).  

Producing/Developing Company:

Ostarine by GTx Inc.

[Currently this is the only form available, other than underground preparations]

Availability: Low (Only available from one underground supplier)

Counterfeited: Never (but I suspect we’ll be seeing them soon) 


  1. Journal of Pharmacology And Experimental Therapeutics, Vol. 304, Issue 3, 1334-1340, March 2003
  2. Pharmaceutical Research. 2007 Feb;24(2):328-35.
  3. Pharmaceutical Research. 2006 Aug;23(8):1641-58.
  4. GTx Announces That Ostarine Achieved Primary Endpoint Of Lean Body Mass And A Secondary Endpoint Of Improved Functional Performance
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